Lipid acyltransferases are known to be advantageous in food applications. Lipid acyltransferases have been found to have significant acyltransferase activity in foodstuffs. This activity has surprising beneficial applications in methods of preparing foodstuffs.
For instance, WO 2004/064537 pertains to a method for the in situ production of an emulsifier by use of a lipid acyltransferase and the advantages associated therewith.
International Patent Application No. PCT/IB2001/000558 relates to the expression of lipid acyltransferases in (heterologous) host cell and is incorporated herein by reference.
Heat treatment in the production of long-life products is often called “sterilisation”. This means that the product is exposed to such powerful heat treatment that all relevant microorganisms and most of the heat resistant enzymes are inactivated. Such products have excellent keeping qualities and can be stored for long periods of time at ambient temperatures. Many dairies can therefore distribute these products over long distances and thereby find new markets.
Typically two methods are used for the production of sterilised (otherwise known as long-life milk for ambient storage), namely in-container sterilisation or UHT treatment followed by aseptic packaging in packages protecting the product against light and atmospheric oxygen. The present invention is applicable to long-life milk produced by any method, e.g. UHT milk.
There are many advantages for the producer, retailer and consumer if the product does not require refrigeration and can be stored for long periods without spoiling.
These products are often called UHT-products, particularly UHT milk or UHT flavoured milks.
Milk exposed to UHT treatment must be of a very good quality. It is particularly important that the proteins in the raw milk do not cause thermal instability, which can be the case if the raw milk is of bad quality. A milk is unsuitable for UHT treatment if it is sour, has the wrong salt balance and/or contains too many serum proteins, typical of colostrum.
When milk is kept at a high temperature for a long time, certain chemical reaction products are formed, which results in discolouration (browning). It also acquires a cooked and caramel flavour, and there is occasionally a great deal of sedimentation. These defects are largely avoided by heat treatment at a higher temperature for a short time. It is important that the optimum time/temperature combination is chosen to enable satisfactory spore destruction while keeping heat damage to the milk to a minimum.
It has been shown that when milk is heated (e.g. pasteurised at 70-80° C. for 5-20 seconds), an effect known as the “cream plug phenomenon” is evident. Heat treatment of milk may be detrimental to the stability of the milk.
The principal constituents of milk are water, fat, proteins, lactose (milk sugar) and minerals (salts). Milk also contains smaller amounts of other substances such as pigments, enzymes, vitamins, phospholipids (substances with fat like properties), sterols and gases.
The many lipids of milk, together forming the ‘milk fat’, have a very complicated composition and structure, even more complicated than most other naturally occurring fats. Typically milk fat consists of triglycerides, di- and monoglycerides, fatty acids, sterols, carotenoids and vitamins (A, D, E and K). Other components include phospholipids, lipoproteins, glycerides, cerebrosides, proteins, nucleic acids, enzymes, metals and water.
Phospholipids are the most surface-active class, as they are amphipolar. As the molecular size is relatively large, they are hardly soluble, neither in water nor in fat. In both liquids they tend to form lamellar bilayers. Phospholipids of milk are generally seen in close connection with proteins, especially when located in the membrane(s) of milk fat globules. The main part of phospholipids in milk is Lecithins, which are surface active at moderate hydrophilicity. Thus lecithin can be seen as a suspending and dispersing agent or as an emulsifier for O/W emulsions as well as for W/O emulsions.
Phospholipids comprises 0.8-1.0% of the natural milk fat. The main types of phospholipids/lecithin in milk are phosphatidylcholine and phosphatidylethanolamine.
Sterols are highly insoluble in water, and show very little surface activity. They easily associate with phospholipids. The cholesterol may be considered an unwanted ingredient in milk when considering the nutritional value of milk. Cholesterol comprises 0.3-0.4% of the natural milk fat.
EP 1 532 863 relates to the use of a phospholipase to treat a cheese milk or a cheese milk fraction.
Tanji et al (Res. Bull. Obihiro Univ., 22 (2001): 89-94) relates to the use of lipases to enhance flavour in butter oil at 40° C.
JP 57-189637 and JP57-189638 pertains to the treatment of milk to produce fermented or acidic milk drinks using phospholipases—where the enzymatic treatment is done at 30-45° C.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.